Embodiments of the subject matter disclosed herein generally relate to methods and devices and, more particularly, to mechanisms and techniques for testing a stage of a multiple stage centrifugal compressor, and specifically testing the portion of the performance curve associated with very low to zero resistance or even a negative suction head.
Centrifugal compressors are utilized extensively in many industries today across a wide variety of applications. An important requirement in the manufacture, sale and delivery of centrifugal compressors is providing a performance curve for the centrifugal compressor that is based on empirical data with as little extrapolation as possible of the performance curve. Using current methods and systems for generating a performance curve for a centrifugal compressor, a prior art test system 100 is configured as shown in prior art FIG. 1. A centrifugal compressor 102 is connected to a gear box 104 and an electric motor 106. The gear box 104 and electric motor 106 are sized based on the requirements of the centrifugal compressor 102. Continuing with the prior art test system 100 example, the outlet 108 of the centrifugal compressor is piped through a control valve 110 and then a process fluid cooler 112 before returning to the centrifugal compressor inlet 114. It should be noted in the prior art example that sensors for recording operating parameters such as, but not limited to process fluid temperature and pressure are placed proximate to the centrifugal compressor outlet 108 and inlet 114.
The centrifugal compressor 102 is then operated with the control valve 110 at different positions such as, but not limited to, ten percent to one hundred percent open in increments of ten percent while data is collected from the sensors associated with the prior art test system 100. The collected data is then used to generate a performance curve for the centrifugal compressor as illustrated in prior art FIG. 2. Prior art FIG. 2 depicts a graph of Head versus Flow and shows the performance curve 202 based on the data collected from the test procedure with the control valve 110 in different positions of almost closed 204, partially open 206 and fully open 208. It should be noted in the prior art test system 100 that the resistance experience by the compressor is at a maximum, based on this test, when the control vale 110 is in the almost closed 204 position and at the minimum obtainable by this prior art test system when the control valve 110 is in the fully open 208 position.
The unknown section 210 of the performance curve is only determinate based on extrapolation with the prior art test system 100 and does not have a unique method of extrapolation. It should be noted in the prior art system 100 that although the control valve is fully open 208, there are still losses associated with the design of the system based on the presence of the components, and their associated losses, of the prior art test system 100. The combination of uncertainty in the extrapolation methods and the errors associated with extrapolation at a boundary condition have led to market pressure to provide empirically produced specifications in the unknown section 210 of the performance and even beyond to a negative head location on the centrifugal compressor performance curve.
Accordingly, it would be desirable to provide designs and methods that avoid the afore-described problems and drawbacks.